The present invention disclosed herein relates to an optical device, and more particularly, to a laser system that may expand the spectrum of a laser pulse and increase peak intensity thereof.
After the invention of the laser in the 1960s, research on industrial applications of the laser actively began in the 1970s. Actually, a laser including a CO2 laser has been utilized for various fields such as industry, medical treatment, communication, and display since 1980.
Also, a solid-state laser has emerged due to the development of a diode laser in 1980's and as the solid-state laser is applied to a field to which a typical gas-state laser is easily applied, a demand for the laser has gradually increased. Thus, laser application fields are becoming very broad, such as an industry field including laser processing, cutting, welding, drilling, trimming, and etching fields, a medical field including dental treatment, spot, tattoo removal, hair removal, laser-assisted in-situ keratomileusis (LASIK), an academic field studying on the interaction of a laser and a material, national defense and culture fields.
The development of an industrial technology needs precision and high productivity in the field in which a laser is used. In response thereto, an ultra-short laser beam is being utilized in various fields, recently. The ultra-short laser beam is generally called a femto second or pico second laser beam.
The ultra-short laser beam has a characteristic that optical energy is focused for a very short time, e.g., about 10−12 s to about 10−15 s to emit light. Thus, the ultra-short laser beam shows a different characteristic from a typical laser beam. For example, since the ultra-short laser beam is irradiated for a shorter time than a time for which heat is transferred to a medium when the beam is irradiated to the medium, it is possible to avoid thermal effect or thermal deformation that appears in typical laser processing.
Since the ultra-short laser beam may process a medium without damage to the surface of the medium, it is being used in fields (semiconductor, electronic chips, and medical treatment) that need precise and micro processing.
However, the ultra-short laser alone has a limitation in intensity in order to be industrially used for the increase in yield and the expansion of a processing area. Thus, it works as a constraint on the expansion of application fields.
A pico second laser beam has been proposed by A. J. DeMaria, D. A. Stetser, and H. Heynau in 1966. The pico second laser beam may be provided through a pico second Nd:glass laser that uses a dye as saturable absorber. A femto second laser beam has been proposed by C. V. Shank and E. P. Ipen in 1974. The femto second laser beam may be generated by using a dye as a gain material. Then, with the emergence of a diode laser, a femto second solid-state laser that uses a mode locking technology has been introduced by D. E. Spence, et al. in 1991. Also, a high-intensity pico second laser using the mode locking technology or saturable absorber has also developed. Also, the ultra-short laser pulse has combined with a chirped pulse amplification (CPA) technology developed by G. Mourou, et al. in 1985 and thus the amplification of the ultra-short laser pulse has become possible, and at present, a high-intensity ultra-short pulse emitted through a multiple amplification stages is being used in many fields. However, since due to the amplification stage, the size of a laser grows, the cost also increases and a specialist for maintaining the amplification stage is needed, there is a constraint on the expansion of an application in the industrial world.